This application claims the benefit of Taiwan application Serial No. 091106436, filed Mar. 29, 2002.
1. Field of the Invention
The invention relates in general to a display apparatus, and more particularly to a display apparatus with a driving circuit in which every three adjacent pixels are coupled to the same data line.
2. Description of the Related Art
Liquid Crystal Displays (LCDs) have been widely used throughout the world because they feature the favorable properties of thinness and lightness and generate low levels of radiation.
FIG. 1 shows a circuit diagram illustrating a conventional LCD panel. The display panel includes a plurality of pixels (P). The pixels are arranged in the form of a matrix on the display panel. The display panel includes an active matrix driving circuit for driving the pixels. The active matrix driving circuit includes a plurality of scan lines (S), a plurality of data lines (D), and a plurality of switching devices. The switching devices are set in the pixels for selectively transmitting the corresponding data signals to the pixels. The switching device can be a thin film transistor (TFT), such as an n-type field effect transistor (n-FET) or a p-type field effect transistor (p-FET). In FIG. 1, the switching device of each pixel includes a thin film transistor. The thin film transistor in each pixel includes a gate electrode, a first source/drain electrode, and a second source/drain electrode. The gate electrode of the thin film transistor is coupled to the corresponding scan line, and the first source/drain electrode is coupled to the corresponding data line. Using the pixel P(m,n) as an example the pixel P(m,n) includes a thin film transistor M1. The gate electrode of the thin film transistor M1 is coupled to the scan line Sm, and the first source/drain electrode of the thin film transistor M1 is coupled to the data line Dn. Each scan line is perpendicular to each data line. Each pixel in the same pixel row is coupled to the same scan line, and each pixel in the same pixel column is coupled to the same data line, as shown in FIG. 1.
FIG. 2 shows the configuration of a conventional active matrix liquid crystal display. The conventional active matrix liquid crystal display includes a display panel 202, an X board 212, and a Y board 214. The display panel 202 includes the pixels and the active matrix driving circuit, as shown in FIG. 1. The Y board 214 is coupled to a plurality of scan drivers 206 set in the tape carrier packages 210. Each scan driver 206 is coupled to the Y board 214 and the corresponding scan lines respectively. The X board 212 is coupled to a plurality of data drivers 204 set in the tape carrier packages (TCP) 208. Each data driver 204 is coupled to the X board 212 and the corresponding data lines respectively. The Y board 214 and the scan drivers 206 are used for enabling the corresponding scan lines through inputting a scan signal into the scan line. When the scan line is enabled, each pixel in the pixel row coupled to the scan line can be turned ON. The X board 212 and the data drivers 204 are used for inputting the data signals to the corresponding pixels through the corresponding data lines when the pixels are turned ON.
The conventional active matrix liquid crystal display has the following disadvantages. First, a large number of data lines are needed. For example, an active matrix display panel has a resolution of 1024×768; that is, the active matrix display panel has 1024 pixel columns and each pixel column has 1024×3=3072 pixels. Therefore, the active matrix display panel must include 3072 data lines. This is a large number of data lines. First, since so many data lines are needed, the pitch between the adjacent data lines must be small. Second, each data line is coupled to the corresponding data driver through the outer lead of the tape carrier package, and it is both difficult and elaborate to connect all data lines to the corresponding outer leads of the tape carrier packages. Third, the aperture ratio of the display panel will be decreased since the number of data lines is so large.
FIG. 3 shows a diagram of a conventional time domain multiplex driving circuit. In the conventional time domain multiplex driving circuit, every two adjacent pixels in the same pixel row are coupled to the same data line. These two pixels are set on the left and right sides of the data line respectively. The pixel set on the left side of the data line is called the left pixel (LP), and the pixel set on the right side of the data line is called the right pixel (RP). The switching devices for the pixels LP and RP are different. Take the pixels LP(m,n) and RP(m,n) as an example. These two pixels are both coupled to the same scan line Sm and the same data line Dn. The pixel LP(m,n) is set on the left side of the data line Dn, and the pixel RP(m,n) is set on the right side of the data line Dn, as shown in FIG. 3. The pixel RP(m,n) switching device includes a thin film transistor M2. The gate electrode of the thin film transistor M2 is coupled to the scan line Sm, and the first source/drain electrode of the thin film transistor M2 is coupled to the data line Dn. The switching device of the pixel LP(m,n) is different from that of the pixel RP(m,n). The switching device of the pixel LP(m,n) includes two thin film transistors M11 and M12. The gate electrode of the thin film transistor M11 is coupled to the scan line Sm+1, and the first source/drain electrode of the thin film transistor M11 is coupled to the data line Dn. The gate electrode of the thin film transistor M12 is coupled to the scan line Sm, and the first source/drain electrode of the thin film transistor M12 is coupled to the second source/drain electrode of the thin film transistor M11, as shown in FIG. 3.
FIG. 4 shows a timing chart for the scan signals of scan lines Sm, Sm+1, and Sm+2 and the ON and OFF status of the corresponding pixels LP(m,n), RP(m,n), LP(m+1,n), and RP(m+1,n) shown in FIG. 3. The method for driving a display panel with the above-described time domain multiplex driving circuit is called a time domain multiplex driving method. When the time domain multiplex driving method is executed, each pixel row is driven in turn by the time domain multiplex driving circuit. The time domain multiplex driving method includes two scanning procedures. The first scanning procedure is to selectively turn on the left pixels of the pixel row by turning on two corresponding TFTs of each of the left pixels and then feeding the corresponding data signals into the respective left pixels. The second scanning procedure is to selectively turn on the right pixels of the pixel row by turning on one corresponding TFT of each right pixel and then feeding the corresponding data signals into the respective right pixels.
Using pixels LP(m,n) and RP(m,n) shown in FIG. 3 as an example, during time period T1, the scan lines Sm and Sm+1 are enabled. The thin film transistors M11 and M12 can be turned ON, and a data signal can be input to the corresponding pixel LP(m,n) through the TFTs M11 and M12. In the time period T2, only the scan line Sm is enabled. The thin film transistor M2 can be turned ON, and a data signal can be input to the corresponding pixel RP(m,n) through the TFT M2.
In the time domain multiplex driving circuit, the above-described disadvantages of the conventional active matrix driving circuit can be improved. If the resolution of the display panel is 1024×768, for example, every two adjacent pixels in the same pixel row are coupled to one corresponding data line of the time domain multiplex driving circuit, and thus only 3072/2=1536 data lines are needed.
However, the conventional time domain multiplex driving circuit disclosed above has the following disadvantage. An equivalent capacitor between the gate electrode and the second source/drain electrode is created when the thin film transistor is turned ON. The output voltage will be lower than the input voltage of the thin film transistor, and the luminance of the pixel may be decreased because of the equivalent capacitor. This effect caused by the equivalent capacitor is called the feed-through effect. The larger the capacitance of the equivalent capacitor is, the larger the difference between the output voltage and the input voltage of the thin film transistor is. Take the pixels LP(m,n) and RP(m,n) shown in FIG. 3 as an example. The switching device of the pixel RP(m,n) includes only one thin film transistor M2 and the switching device of the pixel LP(m,n) includes two thin film transistors M1 and M12. The data signal inputted to the pixel RP(m,n) only through the thin film transistors M2 but the data signal inputted to the pixel LP(m,n) through two thin film transistors, M11 and M12. Therefore, the equivalent capacitor of LP(m,n) is much larger than that of RP(m,n). During driving of the pixels by the time domain multiplex driving circuit, the luminance of the pixel LP(m,n) will be less than that of the pixel RP(m,n) when the data signals of the same magnitude are input to the pixels LP(m,n) and RP(m,n) respectively. Therefore, the luminance of the adjacent pixels may not be the same even when the data signals of the same magnitude are input to the respective pixels. Since pixel LP(m,n) includes two thin film transistors and the pixel RP(m,n) includes only one thin film transistor, the aperture ratio of these two adjacent pixels may not be the same. The luminance of the pixel can be affected by the aperture ratio of the pixel, and because of the feed-through effect and the aperture ratio of the pixel, the display performance of the liquid crystal display would thus be degraded.
FIGS. 5A˜5C illustrate the conventional driving circuit shown in FIG. 3 of the pixels, the pixel columns, and the pixel units respectively. FIG. 5A shows the conventional driving circuit of the pixels, as shown in FIG. 3. In reference to FIG. 5B, the method used for inputting data signals into the corresponding pixels of the color display panel is, taking the adjacent pixels LP(m,n), RP(m,n), and LP(m,n+1) as an example, to input the data signal for showing red into the pixel LP(m,n), the data signal for showing green into the pixel RP(m,n), and the data signal for showing blue into the pixel LP(m,n+1) respectively. All other pixels in the same column as the pixel LP(m,n) are input with the data signals for showing red. The pixel column is thus called the red pixel column RPC1. In the same manner, all other pixels in the same column with the pixel RP(m,n) are input with the data signals to show green. The pixel column is thus called green pixel column GPC1. All other pixels in the same column with the pixel LP(m,n+1) are input with data signals to show blue; the pixel column is thus called blue pixel column BPC1. Following the same order, the pixel column that includes the pixel RP(m,n+1) is for displaying red, the pixel column that includes the pixel LP(m,n+2) is for displaying green, and the pixel column which includes the pixel RP(m,n+2) is for displaying blue respectively. Therefore, these three adjacent pixel columns are called red pixel column RPC2, green pixel column GPC2, and blue pixel column BPC2 respectively. In reference to FIG. 5C, taking the pixel unit PU1 as an example, pixel unit PU1 includes three adjacent pixels LP(m,n), RP(m,n), and LP(m,n+1). Since the pixel LP(m,n), RP(m,n), and LP(m,n+1) are for displaying red, green, and blue respectively, the displaying color of the pixel unit PU1 can be controlled by controlling the luminance of these three pixels. In the same manner, the displaying color of the pixel unit PU2 can be controlled by controlling the luminance of pixels RP(m,n+1), LP(m,n+2), and RP(m,n+2) respectively. Every three adjacent pixels are grouped into a pixel unit for displaying color, as shown in FIG. 5C.
Taking pixel LP(m,n) of pixel unit PU1 and pixel RP(m,n+1) of pixel unit PU2 as an example, in FIG. 5C, both pixels LP(m,n) and RP(m,n+1) are for displaying red. However, because the degree of the feed-through effect and the aperture ratio of these two pixels are different, the luminance of these two pixels can be different even when the magnitude of the data signals input to these two respective pixels are the same. In the same manner, the luminance of the pixel of pixel unit PU1, which is for displaying green, and the corresponding pixel of pixel unit PU2 and the pixel of pixel unit PU1, which is for displaying blue, and the corresponding pixel of pixel unit PU2 cannot be the same even when the respective input data signals are of the same magnitude.
Therefore, the color of the two adjacent pixel unit columns cannot be the same when inputting data signals of the same magnitude into these two adjacent pixel unit columns. This phenomenon is called odd-even line, and it may result in degradation of the liquid crystal display performance.